The present invention concerns a process for producing an aromatic polycarbonate and, more in particular, it relates to a process for producing a high molecular weight aromatic polycarbonate with less coloration during molding at high temperature.
As a process for producing an aromatic polycarbonate, there has been known a process for producing a high molecular weight aromatic polycarbonate by reacting an aqueous alkali solution of a dihydric phenol and phosgene in an organic solvent thereby forming a low molecular weight polycarbonate oligomer having chloroformate groups (--OCOCl) and then polymerizing the oligomer in a highly emulsified state (Japanese Patent Publication No. 37-2198). The process has a merit capable of rapidly forming a high molecular weight aromatic polycarbonate, but the separation of water layer from organic layer, which is done in order to remove the water poluble impurity from a polymer solution, is too difficult, because an extremely stable emulsified state is formed. In addition, molding conditions for the polymer produced by this method are restricted since the resultant polymer shows poor heat stability and suffers from coloration upon molding at high temperature even after sufficient washing for purification.
Further, there has been known a method of using a tertiary amine as a catalyst upon polycondensation (refer to U.S. Pat. No. 3,775,601). However, although a high molecular weight aromatic polycarbonate can be obtained easily by usual stirring in this process, the tertiary amine reacts with the chloroformate to form thermally instable urethane bonding and, accordingly, the polymer suffers from coloration upon molding at high temperature and products with good color can not be obtained.